Curing Properties of Urea-Formaldehyde and Melamine-Modified Urea-Formaldehyde Resins with Dynamic Mechanical Analysis

摘要

Dynamic mechanical analysis (DMA) method was used to study the curing parameters of urea-formaldehyde (UF) and melamine-modified urea-formaldehyde (MUF) resins. Catalyst level, resin formulation, melamine level, curing temperature and time interval between catalyst addition and DMA tests were examined. The gelation in UF resins preceded the vitrification by a relatively long, low modulus period, indicating that gelations occur perhaps very early due to certain UF polymer resin fractions formed in resin synthesis. The gel time and the cure time of UF resins measured by DMA were well correlated with the catalyst level and the resin temperature, and the cure rate was strongly affected by the time interval between catalyst addition and DMA tests. Cure times of MUF resins were longer than those of UF resins increasing with melamine levels. The higher extent of polymerization attained of UF base resins in MUF resin synthesis increased the cure rate. The rigidity and thermal stability of cured MUF resins were higher than those of UF resins, especially at higher curing temperatures. The rigidity and cure rate of MUF resins were highly affected by melamine levels and formaldehyde/urea (F/U) mole ratios.